1. Field of the Invention
The present invention relates to a measuring method for testing semiconductor integrated circuits (referred to as ICs hereinafter).
2. Description of the Related Art
A conventional IC measuring method will be described with reference to FIG. 6. An IC 1 has sixty-four external leads 15. The external leads 15 are connected through corresponding cables 16 to a test head 5 in a measuring apparatus 7. The test head 5 includes at least sixty-four pin-electronic elements 17 each of which has a comparator 18 and a driver 19. Each of the external leads 15 of the IC 1 is connected to a corresponding pin-electronic 17. The measuring apparatus 7 further comprises a controller 8 which is connected to the test head 5 by cables 6.
When the IC 1 is tested, a power source 20 in the controller 8 supplies power through the cables 6, the test head 5 and the cable 16 to power-receiving external leads 15 of the IC 1. Then, a test pattern generator 22 in the controller 8 sends Hi-level and Lo-level signals to the external leads 15 which are related to the test. The output signals from the IC 1 are measured by a measuring unit 21 in the controller 8.
Usually, several tens of different functional tests are performed for one IC 1, and different sets of external leads 15 are used to receive signals for different functional tests. The external leads 15 to which signals are not sent are held at a predetermined electric potential.
In the conventional art, all the external leads 15 of an IC 1 to be tested are connected to the corresponding pin-electronic elements 17 in the test head 5, as described above. Thus, the test head 5 have at least as many pin-electronic elements 17 as the external leads 15 of an IC 1. Therefore, for testing a large IC halving a large number of external leads, a measuring apparatus having a small number of pin electronic elements 17 cannot be used. In such a case, either pin-electronic elements 17 have to be added to the apparatus or a large measuring apparatus having a large number of pin-electronic elements 17 has to be employed.
Especially, when a plurality of IC are tested at one time in-order to improve measuring efficiency, at least as many pin-electronic elements as the total number of the external leads are required since all the external leads of the ICs have to be connected to pin-electronic elements in one-to-one relationship. Inevitably, measuring apparatus becomes large. For example, when four IC each of which has sixty-four external leads are to be tested at one time, 256 (4.times.64) pin electronic elements are needed.